1. Field of the Invention
The present invention relates to cationic resins and to the use of these resins as pigment grinding vehicles in pigment pastes and in a method of cationic electrodeposition.
2. Brief Description of the Prior Art
In the formulation of paints and especially electrodepositable paints, an important factor is the introduction of pigments into the paint. The pigments are typically ground in a pigment grinding vehicle, which acts as a dispersing agent, to form a paste and the resultant pigment paste is blended with the main resinous vehicle and optionally diluents to form the paint. For electrodeposition paints, the pigment grinding vehicle preferably is a resinous material having the same charge as the main resinous vehicle, so that it will electrodeposit with the main resinous vehicle. Typical pigment grinding vehicles for cationic electrodeposition are quaternary ammonium salt group-containing resins such as described in U.S. Pat. Nos. 4,007,154 and 4,186,124.
High film build electrodeposition resins are becoming increasingly popular in the automotive industry where they can be deposited as primers without requiring the application of an intermediate coating of primer-surfacer before application of the top coat. Unfortunately, these high film build electrodeposition primers are difficult to apply with good appearance. They are often rough and have pinholes, particularly over metal substrates such as galvanized steel. Although many factors contribute to the appearance of the electrodeposited film, the pigment grinding vehicle is believed to contribute significantly in this regard.
Also, it is difficult to synthesize a pigment grinding vehicle which produces smooth films while maintaining high rupture voltages. The rupture voltage is the lowest voltage at which the electrodepositing film will rupture. High rupture voltages are desirable because the higher the voltage one can electrodeposit without rupturing the film, the higher the throwpower. High throwpowers are desirable because they enable a film to be electrodeposited in areas shielded from the counter electrode.